Next-generation wireless personal communication networks will be required to co-exist with fiber-optic based broadband communication networks, which should become far more ubiquitous in the near future. These broadband systems (such as B-ISDN/ATM and ATM LAN) will offer constant bit-rate (CBR), variable bit-rate (VBR), available bit-rate (ABR) and packet transport services designed to support a range of voice, data, video, and multimedia applications. In order to avoid a serious mismatch between future wireline and wireless networks, it is necessary to consider broadband wireless systems with similar service capabilities. Personal communication networks introduced into the future multimedia application scenario should provide new service features such as high- speed transmission, flexible bandwidth allocation, VBR/CBR/packet modes, quality-of-service (QoS) selection, and so forth.
The overall technical approach of the present invention is based on the recognition that ATM has recently emerged as the predominant switching and transport technology for wide and local area broadband networks to be deployed during the next several years. This means that it is desirable for the next-generation wireless personal communication network to provide similar ATM type service capabilities to the extent possible using radio medium. While certain quantitative limits on bit-rate or quality-of-service may have to be accepted for the wireless network, the availability of qualitatively equivalent service classes in a seamless manner would provide significant benefits of uniformity to network operators, service providers and terminal designers.
There are several basic: problems that must be addressed for the development of ATM-based broadband wireless networks, including:
1. High-speed radio transmission consistent with service requirements of future terminals. Typical video and multimedia services may require transmission bit-rates .about.1-10 Mbps, a channel speed that is significantly higher than that being considered for first-generation wireless systems. PA1 2. Medium access control (MAC) methods that provide relatively transparent multiservices capabilities similar to ATM over the inherently shared wireless medium. Service classes to be supported include constant bit-rate (CBR), variable bit-rate (VBR) and packet data, each with reasonable quality-of-service parameters. PA1 3. Wireless data link protocols for interfacing the relatively unreliable high-speed radio links to the fixed broadband (ATM) network with a minimum of protocol conversion. PA1 4. Signaling and transport protocol modifications necessary to support mobility and new personal communication services in the wireless network.
The present invention provides a solution for the wireless ATM medium access control method referred to in item 2 above.
In an article by D. Raychaudhuri et al entitled "ATM-Based Transport Architecture for Multiservices Wireless Personal Communication Networks" in IEEE Journal on Selected Areas in Communication, vol. 12, no. 8, October 1994, pages 1401 to 1414, there is a basic systems level description of a wireless ATM system. The present invention concerns a novel embodiment of a medium access control useable in systems such as that described in the Raychaudhuri et al article. Specifically, the invention describes a dynamic TDMA (time division multiple access)/TDD (time division duplexing) method for provisioning of ATM transport services on a wireless channel.
In U.S. Pat. No. 4,491,947 there is described a method for dynamic scheduling of integrated circuit switching and packet switching in a multibeam satellite switched time division multiple accessed environment. The scheduling is performed onboard the satellite by a scheduler under the direction of a controller. For each time slot, a least cost assignment is applied for each slot.
U.S. Pat. No. 4,641,304 describes a particular method of dividing time frames into message slots containing mini-slots for retransmission of data packets.
In U.S. Pat. No. 4,897,834 a bit oriented communications network is described where each node of the network broadcasts in time slots in a round robin fashion.
In U.S. Pat. No. 4,937,822 an adaptive time division multiple access communications system is illustrated which maintains different frequencies between nodes of a communication system. The frequency at which the transmissions are made charges according to the signal quality. The TDMA system used relies on a frequency/time slot independent of those in other time slots.
In U.S. Pat. No. 5,012,469 an adaptive hybrid multiple access protocol dynamically switches among contention (ALOHA), reservation and fixed assignment (TDMA) protocols as a function of the traffic of a channel.
In U.S. Pat. No. 5,065,398 a TDMA satellite communications arrangement is described. Data to be transmitted is divided into subpackets and then the subpackets are transmitted in predetermined time slots.
In U.S. Pat. No. 5,172,375 a combination of fixed assignment, random and demand access methods are used in a satellite communication system. In the present invention, data is transmitted by a TDMA access method.
The above patents provide a broad background of the art. Some of these patents, for example, refer to satellite systems. In general, these patents do not refer to ATM networks, multimedia applications or microcellular wireless systems.
In U.S. Pat. No. 5,384,777 there is described a medium at access control (MAC) protocol for wireless radio access for a plurality of remote stations to a base station on a LAN.
The present invention provides an advance beyond the teachings found in the above patents by providing ATM compatibility with multiservice/quality of service for services including packet ABR, UPC-based VBR or isochronous CBR. The disclosed MAC is directed at ATM compatibility at both service and cell levels which has not been achieved heretofore.